1. Field of Invention
This invention relates to the use of zirconium in a multi-layer thin film metallic structure. More particularly, the use of zirconium as an adhesive layer between a ceramic or polyimide substrate and a copper or aluminum layer is disclosed.
2. Background Information
As the integrated circuit density continues to increase towards Very Large Scale Integration (VLSI), the increases in both the input/output (I/O) counts and wiring densities have placed stringent demands on the multi-layer chip packaging technologies. In order to interconnect large numbers of integrated circuit (IC) chips, each containing high densities of I/O terminals, the ability to produce fine and precise patterns with great reduction of lead pitch is becoming increasingly crucial to the success of future VLSI packaging technologies.
Today's thick film multi-layer ceramic (MLC) technology has reached a limit, because the silk screening method is not capable of producing patterns with a minimum line width of less than 3 mils, and the sintering process is plagued with large dimensional tolerances. Thick film MLC technology by itself is not enough to meet the requirements for advanced VLSI packaging technology.
One method of providing inter-chip wiring and I/O interconnections utilizes thin film polyimide packages on top of a conventional MLC base. The structure consists of a MLC substrate as a base to supply current and mechanical support and thin film layers processed on top of the MLC base to provide inter-chip wiring and to fan-out the semiconductor chip contacts to the thin film wiring layers. Among the materials tested, the use of polyimide as a low dielectric insulating layer between finely patterned high conductivity copper layers achieves the best performance.
One of the problems, however, with the use of copper for fine wiring, is that a pure copper to polyimide bond is not capable of withstanding the subsequent process and handling steps. Therefore, it is desirable to provide a method for enhancing the adhesion between copper and a polyimide substrate.